1. Field of the Invention
The present invention relates to a means for monitoring the condition of electric devices with current-breaking contacts, in particular high voltage cirucit-breakers.
2. Prior Art
Most high voltage circuit-breakers are dismantled for maintenance unnecessarily often. The reason for this is simple to understand: It is better to intervene once to many than running the risk of a circuit-breaker losing its function, thus causing damage to the whole switchgear. The problem so far has been to correctly determine when it is time for service. For example, for circuit-breakers in normal distribution networks with few interruptions each year, it is the operating device of the circuit-breaker and the condition of said device that need to be checked ("exercised", lubricated), whereas the breaking poles in principle never have to be touched. For circuit-breakers in very heavy operation in industry the situation may be the reverse.
A device for monitoring the condition of circuit-breakers, proposed in the patent publication DE-OS No. 27 27 378, includes a current transformer as current sensing member. Such a transformer involves relatively high costs and, in addition, for reasons of space, is difficult to locate in modern compact switchgear cubicles.
It is further known, from U.S. Pat. No. 4,101,826, to use reed contacts for indicating fault currents. In that connection, however, the reed contact is used only for setting a flip-flop which in turn starts a pulse transducer, whereby a timing circuit resets the flip-flop after a definite number of pulses. No registration of current quantity, arcing energy or other measurement values for determining the contact wear takes place in this device.